X-ray tomography system with gantry pivot and translation control

ABSTRACT

An improved, portable X-ray tomography system is disclosed wherein lateral movement of the various tomography components relative to a stationary patient during a scanning procedure is precisely controlled by mechanical displacement means which, in tarn, is coupled to electro-mechanical means for simultaneously measuring and monitoring the amount of the displacement.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.08/193,783, filed in the name of Gilbert W. McKenna and entitled "X-rayTomographic Scanning System" (Attorney's Docket No. ANA-30); U.S. patentapplication Ser. No. 08/193,696, filed in the name of Gilbert W. McKennaand Ronald E. Swain and entitled "Tomographic Scanner Having Center ofRotation for all Physics" (Attorney's Docket No. ANA-31); and U.S.patent application Ser. No. 08/193,782, filed in the name of Gilbert W.McKenna and entitled "Stabilized, Cantilevered, Patient Trauma TableSystem" (Attorney's Docket No. ANA-58), all filed simultaneouslyherewith and assigned to the present assignee.

FIELD OF INVENTION

The present invention relates generally to X-ray tomography Systems and,more specifically, to a portable system for supporting and moving atomography gantry assembly relative to a stationary support forsupporting the object being canned in order to provide limited,precisely controllable and measurable translation of the gantry assemblyparallel to the stationary support, and also to provide limited,precisely controllable tilting of the gantry assembly relative to theobject being scanned.

BACKGROUND OF THE INVENTION

The present invention is an improvement in portable X-ray tomographysystems such as those described in U.S. Pat. Nos. 4,928,283 (issued May22, 1990 to Bernard M. Gordon for X-Ray Tomography Apparatus, andassigned to the present assignee) and 5,109,397 issued Apr. 28, 1992 toBernard M. Gordon et al. for X-Ray Tomography Apparatus With LateralMovement Compensation, also assigned to the present assignee); andhelical scan tomography systems such as described in GermanGebrauchsmuster File No. G 87 03 190.6, filed by Siemens AG andpublished Aug. 11, 1988, all three documents being incorporated hereinby reference.

Tomography systems have been used for many years to create images ofcross-sectional slices through object, and are particularly used as adiagnostic aid. CT (computed tomography) scan systems usually include agantry assembly comprising a disk mounted for rotation within a gantryframe. In third generation machines, the disk supports X-ray imagingcomponents including an X-ray source and X-ray detectors that rotatewithin a stationary frame. In fourth generation machines the X-raydetectors are secured equiangularly around the stationary frame whilethe source rotates with the disk relative to the detectors. In bothtypes of systems, the source may provide periodic X-ray pulses, oralternatively, continuous-wave (CW) X-rays. The disk of the gantry isnormally adapted to rotate through a full 360° rotation so that theimaging components secured to the disk rotate through a plurality ofincremental positions where a corresponding series or set of readings(called "views") by the detectors are made. The number of photonsabsorbed along the various paths through the object, during eachsampling period defining each view or set of readings is a function ofthe absorption characteristics of the portions of the object along eachpath during each set of readings. Thus, a plurality of views are takenthrough the portion of an object disposed within the common plane ofrotation of the X-ray paths (hereinafter the "scanning plane"). Thedetectors generate a corresponding plurality of analog informationsignals representative of X-ray flux detected by the detectors duringeach sampling period or projection view.

The output analog information signals of the X-ray detectors acquiredfrom all of the views of the 360° rotation, i.e., through all of theincremental angular positions of the 360° rotation within the scanningplane, are processed, typically through a back projection processingtechnique, so as to create an image of the slice of the interiorstructure of the object exposed to the X-rays: In some CT scanners,provision is made to move the patient support while performing a scan inorder to provide a helical scan so as to increase the scanned volume.

An important consideration in CT scanning has always been the accurateand consistent alignment of the tomography components and the patientboth throughout the rotation and over the course of many scans andpatients. Misalignment or movement can negatively influence the data ofan entire scan. In order to deal with this factor, manufacturers ofprior art CT scan apparatus typically have produced a very large andmassive machine which includes a heavy gantry assembly for supportingthe tomography components. The handling of this weight requiresadditional mass in the remainder of the apparatus and typically a largeapparatus overall. The rotating disk supporting at least the X-raysource is typically rotatably supported in a excessive, finely-machinedbearing assembly, and an extremely massive and heavy support system isprovided for supporting the gantry assembly and tomography components.The very massiveness of these systems helps to minimize vibration andother lateral mechanical movements, which, for example, can occur withwear between parts moving relative to one another.

But such massive systems are also extremely expensive to build and oncelocated and constructed for use are extremely difficult to relocate.They require large amounts of floor space and thus can not be used inspace limited environments. Thus, use of such systems, for example,within the operating theater are impractical. The result is that a verypowerful data gathering diagnostic system is not readily available to asurgeon when such data might be very helpful, or to trauma units whenmovement of the patient should be minimized.

One ramification of the extra size and mass of these machines has beento provide a fixed gantry assembly so as to require a movable patienttable, as the weight of the patient and the patient table is typicallymuch less than the weight of the gantry assembly and its rotatingcomponents. A movable patient table is used not only to properlyposition the patient in the desired location relative to the fixedgantry assembly so that a scan can be performed through a select portionof the patient's body; but in the case of machines capable of performinghelical scans, to move the patient parallel to the rotation axis(referred to as the "Z-axis") of the tomography imaging components,while the components are rotating about the patient. But, the apparatuswhich has resulted from these various requirements has been typicallylarge, heavy, expensive, and difficult to relocate. It has required alarge amount of floor space and thus can not be used in space-limitedenvironments. A further disadvantage caused by the size and weight ofthese apparatuses has been the wear experienced in the moving partsthereof. Moreover, in the course of repositioning a movable patienttable for successive scans or a helical scan, the momentum of themovement of the table can result in patient movement during the scanresulting in erroneous scanning data. This problem can be especiallyacute when the table moves abruptly at the beginning or end of a scan.

At least one three dimensional CT scanning system has been suggested inGerman Gebrauchsmuster File No. G 87 03 1906 (described above) in whichthe tomographic elements move through a helical path about a stationarypatient table. As described in the document, a rotating ring supportsthe X-ray source and X-ray receiver. The rotating ring is provided withhelical screw threads so that as the ring rotates within a shell duringa scan it simultaneously moves parallel to the patient table so that thering moves in a helical manner along the length of the patient table andso that a high three-dimensional volume can be measured. The dataacquired during a three dimensional scan male it possible to reconstructlarge volume images. However, the movement of the rotating ring isconfined to helical movement so that the system is only capable ofthree-dimensional scanning. Additionally, while the patent suggeststhat, depending on system design, it is possible to reconstruct imagestaken during the three-dimensional scanning process for any theoreticalrotating ring inclination (layer angle) on the basis of data takenduring the scan even through the scanning plane established by the ringcan not be-tilted. This would require the ring to be laterally displacedparallel to the orientation of the patient table over a large distance.For example, to obtain data equivalent to a 45° inclined angle, therotating ring would have to transverse a distance equal to the distancebetween the source and detectors exposing the patient to excessiveamounts of X-rays over a large period of time. Further, the ring appearsto be large, and unnecessarily massive. The system therefore would notbe practical as a portable system.

The portable tomography apparatus described in U.S. Pat. No. 4,928,283(Gordon) represents a significant improvement in the state of the art byproviding an apparatus with a high degree of mobility. The tomographycomponents are supported on a structure that also serves to support aremovable patient table. The gantry assembly is movable between a firstposition where the table is disposed within the gantry and a scan can beperformed on a patient disposed on the patient table and a secondposition where the gantry assembly is oriented 90° to the first positionso that it can be more easily transported and stored. The gantryassembly can be tilted The support structure in the Gordon patent alsoprovides means for rotating the tomography components about the Z-axisand means for moving the tomography components linearly along the Z-axisrelative to the table when the tomography components are oriented in thefirst direction. The patent suggests that the apparatus is thus capableof helical scanning.

The apparatus of the Gordon patent is therefore an improvement over themuch larger, essentially immobile tomography systems of the prior art,With the Gordon apparatus, the tomography system can be brought to thepatient, for example, instead of vice versa. But, the apparatus of theGordon patent is still larger and less maneuverable than desired becausethis apparatus necessarily incorporates the support structure for thepatient table. Furthermore, this apparatus requires transferring apatient to the special removable patient table, which inhibits use ofthe apparatus at critical times such as during surgery, or duringemergency situations. In addition, precise control and measurement ofthe position of the gantry assembly relative to the patient is anelusive problem, since reducing the overall weight and mass of thesystem increase the amount of vibration and mechanical noise to whichthe system will be subject as the components rotate during a scan.

U.S. Pat. No. 5,109,397 (Gordon et al.) attempts to overcome some of theproblems endemic to a portable tomography system by incorporating meansfor providing error information at incremental angular positions andmeans for compensating the data derived from the analog informationsignals. Another type of measurement system for providing such errorinformation is described in U.S. patent application Ser. No. 08/162,653filed on Dec. 6, 1993 in the names of Bernard Gordon, et al., for"Apparatus for and Method of Measuring Geometric, Positional andKinematic Parameters of a Rotating Device" (Attorney's Docket No.ANA-21) and assigned to the present assignee. It remains desirable,nevertheless, to reduce or eliminate misalignment errors in portabletomography systems through more accurate control and measurement of theposition and orientation of the tomography components.

It is desirable to provide an improvement over the X-ray systemdescribed in U.S. Pat. No. 4,928,283 (Gordon), by providing an improvedX-ray tomography system with translation a pivoting control so thatprecise positioning of the components relative to a stationary patienttable can be easily accomplished.

OBJECTS OF THE INVENTION

Accordingly, it is a general object of this invention to provide atomography apparatus which substantially reduces or overcomes theabove-noted problems.

More specifically, it is an object of this invention to providetomography apparatus with means for precisely controlling and measuringthe position of the scanning plane vis-a-vis a stationary patient duringa scanning procedure.

Another object of this invention is to provide a portable tomographyapparatus with means for precisely controlling and measuring thelongitudinal position of the gantry assembly relative to thelongitudinal axis of a patient's body or limb.

And another object of this invention is to provide a portable tomographyapparatus with means for precisely controlling and measuring the tiltingof the gantry assembly relative to the longitudinal axis of a patient'sbody or limb.

It is also an object of this invention to provide a portable tomographysystem which is readily adaptable for use with a patient in either arecumbent or a sitting position.

A further object of this invention is to provide a portable tomographysystem which is independent of the patient support means.

Specifically, it is an object of this invention to provide a portabletomography apparatus wherein lateral translation of the gantry assemblyrelative to the support structure is regulated by mechanicaldisplacement means which, in turn, is coupled to electro-mechanicalmeans for simultaneously measuring and monitoring the amount of thedisplacement.

Still another object of this invention is to provide a portabletomography apparatus capable of carrying out either a sequence ofprecisely controlled individual X-ray scans or a continuous, helicalscan.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the apparatuspossessing the construction, combination of elements and arrangement ofparts exemplified in the following detailed disclosure and theaccompanying drawings, and the scope of the application of which will beindicated in the claims.

SUMMARY OF THE INVENTION

The present invention comprises tomography apparatus wherein limitedlateral movement of a gantry assembly relative to a stationary patientis precisely controlled by coupling mechanical displacement means toelectro-mechanical means for simultaneously controlling and measuringthe amount of the displacement. A support structure for the gantryassembly preferably comprises a cat-like apparatus on wheels beingadapted to: support a translatable and pivotable gantry assembly so asto provide limited, precisely controlled and monitored lateral movementof the gantry assembly relative to the patient and the supportstructure; and limited, precisely controlled tilting of the gantryassembly relative to the axis of a patient's limb or body. The resultingtomography system is compact, readily mobile, and easily maneuverablewhile at the same time generating highly accurate and dependablescanning data.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic perspective view of the tomography apparatus ofthe present invention illustrated in relationship to a state patienttable;

FIG. 2 is a schematic end view of the tomography apparatus and patienttable illustrated in FIG. 1;

FIG. 3 is a schematic side view of the tomography apparatus and patienttable illustrated in FIG. 1;

FIG. 4 is a schematic side view of the tomography apparatus, similar toFIG. 3, but shown in use with a patient chair and arm support;

FIG. 5 is an enlarged, schematic, partly cutaway isometric view of themechanical displacement mechanism used to achieve lateral movement ofthe gantry assembly and of the associated electro-mechanical system formeasuring and monitoring the amount of the displacement; and

FIG. 6 is an enlarged, schematic, isometric side view of the tomographyapparatus of FIG. 1 illustrating the relationship of the mechanicaldisplacement mechanism of FIG. 5 relative to the tomography apparatusand also illustrating the tilt control mechanism of this invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show an X-ray tomography apparatus 10 generally including adoughnut-like gantry assembly 12 mounted on a movable cart apparatus 14.As schematically shown in FIG. 2, gantry assembly 12 comprises astationary annular frame 28, and a disk 30 mounted for rotation withinthe annular frame 28 and supporting conventional tomography components,typically including an X-ray source, a plurality or array of X-raydetectors diametrically opposite the X-ray source, a power source, andother components as described in U.S. Pat. No. 4,928,283. For additionaldetails relating to the gantry assembly see copending U.S. patentapplication Ser. No. 08/193,783, filed in the name of Gilbert W. McKennaand entitled "X-ray Tomographic Scanning System" (Attorney's Docket No.ANA-30); and U.S. patent application Ser. No. 08/193,696, filedsimultaneously herewith in the name of Gilbert W. McKenna and Ronald E.Swain and entitled "Tomographic Scanner Having Center of Rotation forall Physics" (Attorney's Docket No. ANA-31), assigned to the presentassignee, and incorporated herein by reference. In order to protect andconceal the components distributed around the frame of gentry assembly12, a skin or cover 24 of an X-ray transparent material (shownschematically in FIG. 1), such as a polycarbonate plastic or the like,may be provided and secured in place by a plurality of bands orfasteners 26 distributed around the circumference of the gantryassembly. Means (not shown) are provided for rotating the tomographycomponents mounted on gantry assembly 12, such as the means described inU.S. Pat. No. 4,928,283.

As best seen in FIGS. 1 and 2, cart apparatus 14 is generally of aU-shaped configuration comprising a transverse base member 16 supportedon a plurality of wheels 18, upwardly projecting wall members 20 and 22,which may be either extensions of or fastened to base member 16, andmeans for supporting gantry assembly 12 on wall members 20 and 22. Inplace of wheels 18, any equivalent multi-directional movement or rollingmeans, such as ball-and-socket rollers, may be substituted. In apreferred embodiment, wall members 20 and 22 include inwardly slopinglower portions (as best seen in FIG. 2) such that wall members 20 and 22together with base member 16 comprise a protective cradle for the lowerhalf of gantry 12 which flanks the outer circumferential walls of thegantry assembly. One or both wall members 20 and 22 further comprise agantry displacement mechanism 70, generally indicated in FIG. 1 (anddescribed in greater detail in connection with FIG. 5), wherein aportion of which is visible as rod members 80, and a gantry tilt controlmechanism (not seen in FIGS. 1 and 2, but described in greater detailhereinafter in connection with FIG. 6).

For reference purposes, FIGS. 1-3 also show a separate, movable, X-raytransparent patient table or gurney 40 generally comprising a transversebase member 42 supported on a plurality of wheels 44 in combination withupright support members 46 supported on base member 42 at the lower endsthereof. Members 46 in turn support table means 48 at their upperextremities. It will be appreciated that patient table 40 may instead bestationary, in which case no wheels 44 would be needed, without in anyway affecting the operation of the tomography apparatus of thisinvention. In a preferred embodiment, upright table support members 46may comprise telescoping tubes or similar means by which the height ofthe foot and head ends of table means 48 above the floor can be readilyand independently adjusted by conventional automated or manual means.Such table height adjustment means facilitates positioning a patient atthe center of the tomography apparatus, as better seen in FIG. 2 wherethe dotted outline of patient support member 56, as described below,indicates the table in the elevated position. In another preferredembodiment, as seen in FIG. 2, table means 48 may comprise two laterallyextending, grooved side or rail members 52 and 54 and a flat or curvedpatient support member 56 adapted along its lateral edges to be slidablyengaged by the grooves of members 52 and 54. The table 40 includes acoupling mechanism generally indicated at 58 in FIG. 3. Such a patienttable or gurney specially adapted for use in combination with thetomography system of this invention is described in a copending U.S.patent application Ser. No. 08/193,782, filed simultaneously herewith inthe name of Gilbert W. McKenna and entitled "Stabilized, Cantilevered,Patent Trauma Table System" (Attorney's Docket No. ANA-58),assigned tothe present assignee and incorporated herein by reference.

Thus, in preparation for a CT scan, as best seen in FIGS. 1 and 3, cart14 carrying gantry assembly 12 and one end of table 40 would be movedtogether and joined by mechanism 58. Table means 48, if necessary, wouldbe elevated to the desired height for centering with respect to gantryassembly 12. Then, patient support member 56 carrying the subjectpatient would be slid into the inner, annular region of gantry assembly12 for generally positioning the patient. Once the patient is thusinitially positioned vis-a-vis the tomography apparatus, furthermovement of the patient or patient table is unnecessary with theapparatus of this invention. Instead, the gantry displacement mechanism70 is capable of limited, controlled lateral translation of gantryassembly 12 generally along the longitudinal axis of the table in orderto generate the sequential X-ray data needed for large volume andhelical scan imaging. In one embodiment of this invention, therefore,X-ray imaging is performed stepwise in conjunction with incremental,precisely measured, discrete displacements of the gantry assembly withrespect to the patient, which displacements are effected by briefly andrepeatedly activating the gantry displacement mechanism. In analternative embodiment, X-ray imaging can also be carried outcontinuously as a helical scan by activating the gantry displacementmechanism for gradual, continuous and precisely measured lateraldisplacement of the gantry assembly while the tomography system is inoperation with the disk 30 rotating within the annular frame 28.Although a patient table such as that illustrated in FIG. 1 isparticularly well adapted to performing CT scans with the apparatus ofthis invention, as described above, this invention is not to beconstrued as being limited in any way to use in combination with patienttable 40 as described above. It should be appreciated that thetomography apparatus of this invention has utility with other types ofpatient tables and with so other types of patient supports, such as achair as illustrated in FIG. 4.

FIG. 4 shows a plan view of an alternative utilization of the tomographyapparatus of this invention, again wherein corresponding numbersidentify corresponding members. As shown in FIG. 4, limb support means60, comprising a frame 62 supporting a limb platform 64, is mounted oncart 14. The tomography apparatus thus adapted is suitable forperforming CT scans on a patients limb, such as an arm, while thepatient sits or reclines alongside can 14.

FIG. 5 shows an enlarged, partially cutaway view of the gantrydisplacement apparatus as of this invention. Preferably a pair ofidentical gantry displacement apparatus 70, one being shown in FIG. 5 asbeing fixed along one side thereof to base or surface member 72 forillustration, are respectively adapted to be incorporated into orsecured to the wall members 20 and 22 of cart 14 as describedhereinafter. Each displacement apparatus 70 generally comprises anelongated ball screw element 74, connected to drive means such as areversible drive electric stepping motor 76, and displacement member 78functioning in cooperation with screw element 74, such as a ball nut,and connected to the gantry assembly 12. Displacement member 78 isadapted for two-way movement along a track generally defined by screwelement 74. The movement track has a length that is somewhat less thanthe width of cart 14. Screw element 74 and the associated displacementmember 78 are at least partly enclosed by housing means 90. In oneembodiment, electric stepping motor 76 may be mounted externally of onewall of housing means 90 and connected to screw element 74 through anaperture in that housing wall. For example, a stepping motor having 200steps per five millimeters parts a very fine adjustment resolution of0.001 inches/step. Housing means 90 may further comprise apertures 92 intwo opposite end walls in order to accommodate the opposite ends of aguiding rod member 80 as hereinafter described. As seen in FIG. 5,displacement member 78 comprises an internally threaded block whichengages screw element 74 such that, as motor 76 rotates screw element 74in a clockwise direction, member 78 is moved along the screw element ina first direction, and, as motor 76 rotates screw element 74 in acounterclockwise direction, member 78 is moved along the screw elementin a second, opposite direction.

The displacement apparatus may further comprise a guiding rod member 80disposed in a linear bearing comprising a hemispherical or semi-tubularpassageway 82 extending through displacement member 78 (which is coupledto the gantry assembly as described in greater detail in FIG. 6), orthrough another member which is fastened to member 78, wherein thelongitudinal axis of the hemispherical passageway 82 is substantiallyparallel to the longitudinal axis of ball screw 74. The ball screw 74 issuitably journaled in the housing 90 so that it freely rotates inresponse to the operation of the steps per motor 76 without movinglongitudinally. The passageway 82 has a diameter slightly greater thanthat of rod member 80 and may lubricated or be fitted with ball bearingssuch that displacement member 78 slides along rod member 80 as ballscrew 74 is driven by motor 76. As previously noted, the opposite endsof rod member 80 are further supported by passing through a 92 in twoopposite end walls of housing 90. While the two displacement members 78,positioned on respective diametrically opposite sides of the gantryassembly, are preferably oriented parallel to one another, in order toaccommodate minor non-parallel misalignments between the two, apertures92 have diameters slightly larger than that of rod member 80 such that alimited degree of lateral movement or tolerance of rod member 80 isprovided in order to accommodate such minor misalignments during therepositioning the tomography apparatus.

Displacement apparatus 70 further comprises means for measuring theamount of any displacement, so that if necessary it can be monitoredand/or controlled. In a preferred embodiment, the displacementmonitoring means comprises electro-mechanical apparatus, such as apotentiometer 94, suitably biased with a supply voltage (not shown) forproviding a voltage output as a function of the position of thedisplacement member 78. As seen in FIG. 5, potentiometer 94 is securedrelative to the surface member 72, preferably at one end of the screw74. Potentiometer 94 includes a pulley wheel 96 which when turned variesthe resistance of and thus the voltage output of the potentiometer 94. Asecond, follower pulley 96 is preferably secured relative to the surface72, preferably at the other end of screw 74. A cable 98 is looped aroundthe two pulleys and is fixed at one end by suitable means, such as acable connector 88, to the displacement member 78 and its other end to aspring 86 for tensioning the cable, said spring 86 also being connectedto the displacement member 78, preferably via the connector 38 asillustrated. Extremely precise monitoring of the amount and direction ofany movement of displacement member 78 (and thus longitudinal movementof the gantry assembly) is realized by conventional means for monitoringthe electrical voltage across the potentiometer. In a preferredembodiment of this invention, a pair of displacement apparatuses 70 asshown in FIG. 5 are respectively incorporated into or mounted on each ofwall members 20 and 22 of cart apparatus 14 (FIG. 1) so that both sidesof gantry assembly 12 can be moved smoothly and simultaneously.

FIG. 6 shows a schematic side view of gantry assembly 12, with skin 24removed for illustrative purposes mounted on cart apparatus 14 (FIG. 1)and connected to a gantry displacement apparatus 70 similar to thatshown in FIG. 5. As discussed with respect to FIG. 5, in FIG. 6 anelongated ball screw 74 is at least partly housed in housing 90 and isdriven by stepper motor 76 mounted externally of housing 90 andconnected to ball screw 74 through an aperture in the adjacent wall ofhousing 90. The ball screw is suitably journaled in the housing 90 sothat it freely rotates in response to stepper motor 76. The longitudinalaxis of screw element 74 is substantially horizontal and generallyparallel to the longitudinal axis of table 40 (shown in FIGS. 1-3) andlimb support 64 (shown in FIG. 4). Displacement apparatus 70 furthercomprises internally threaded displacement member 78, preferablyincluding a ball screw, which engages screw 74 so as to move toward oraway from motor 76 inside housing 90 as motor 76 rotates screw element74 respectively clockwise or counterclockwise.

Each displacement member 78 is fastened to a corresponding arm 114 (seenin FIGS. 2 and 6). As shown in FIG. 6, one end of each arm 114 ismounted in an aperture 116 of member 78 and secured in place. The twoarms preferably each have longitudinal axes disposed coaxial withrespect to one another. The opposite end of arm 114 is coupled to gantryassembly 12, by means of a fitting assembly 118 located in an uncoveredrecessional area between the front and rear portions 100 and 102 of theannular frame of the gantry assembly 12 and secured so that the gantryassembly and each fitting assembly 118 arm adapted to pivot about thearms 114. Screws 120 or equivalent means may be used to secure by mountassembly 118 to the frame of the gantry assembly. Fitting assembly 118comprises box member 122 having a tubular projection 124 with a centeraperture adapted to receive the opposite end of pivot arm 114.Lubrication or ball bearings may be provided inside the aperture oftubular projection 124 to facilitate rotation of the gantry assembly 12about the pivot arm 114. Box member 122 further comprises an elongatedslot 126 adapted to receive a fixed-length arm member 128. Member 128has one end fixed to the pivot arm 114, and its other, upper end,engaging a ball nut. The member 128 and the corresponding nut remainstationary while allowing the screw 130 to move relative to the nut asthe screw rotate. The latter is suitably journaled at its opposite endsso that it freely rotates in response to motor means 132, such as areversible drive electric stepper motor, mounted to the portion 100 ofthe annular frame, without moving longitudinally within the journals sothat as the screw rotates the entire frame (and therefore the entiregantry assembly) pivots about the arms 114. The upper end of arm 128 isadapted to accommodate two-way movement along a track generally definedby screw element 130. The movement track has a length somewhat less thanthe width of gantry assembly 12. Limited vertical movement of the end ofscrew element 130 opposite motor 132 is provided by vertically extendingslot 134 along the inner side of rear face 102 so as to permit pivotablemovement of the gantry assembly about the arms 114. More specifically,as seen in FIG. 6, the longitudinal axis of screw element 130 may betilted at an acute angle to the horizontal as a function of where alongits length it is engaged by arm 128 so, that as the gantry assemblypivots about the arms 114, any lateral movement of the screw will beaccommodated. As motor 132 rotates screw element 130 in a clockwisedirection, the gantry frame pivots about the arms 114 in a firstdirection. Conversely, as motor 132 rotates screw element 130 in acounterclockwise direction, the gantry assembly pivots about the arms114 in a second, opposite direction. Because arm 128 is fixed,rotational movement of the screw element 130 results in tilting oruntilting gantry assembly 12 and, therefore, the pivot axis of thetomography apparatus is defined by the longitudinal axes of the two arms114. Electrical monitoring means may be used to precisely control thedesired angle of tilting for a particular scanning procedure.

Thus, the apparatus of this invention comprises a readily transportabletomography system which accommodates the needs of the patient and thephysician in a variety of medical environments where prior art systems,because of size, weight, or physical configuration, would have beendifficult if not impossible to use. The tomography system of thisinvention can be utilized, for example, in the operating theater withminimal disruption to the surgical procedure in progress. With thepresent invention, no movement of either the patient or the patienttable is required. Once the cart apparatus carrying the tomographysystem is generally positioned vis-a-vis the patient, the displacementand tilting mechanisms of this invention can be used to preciselycontrol and monitor the plane of an X-ray scan.

Since other changes may be made in the above-described apparatus andmethod without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription shall be interpreted in an illustrative and not in alimiting sense.

Having described the invention, what is claimed is:
 1. An X-raytomographic scan apparatus of the type comprising: (a) an X-ray sourceand X-ray detection means for use in forming a tomographic image; (b) agantry assembly including (i) a non-rotatable support, and (ii) meansfor supporting at least said X-ray source for rotation within a scanningplane about a rotation axis relative to said non-rotatable support so asto perform a tomographic scan; (c) an object support for supporting anobject positioned in the scanning plane during a tomographic scan; saidapparatus further comprising:gantry assembly support means, capable ofbeing fixed relative to said object support, for supporting said gantryassembly so that said gantry assembly is movable along a longitudinalaxis substantially parallel to the object support, said gantry supportmeans comprising at least two support surfaces positioned respectivelyon opposite sides of said gantry assembly; a pair of supports disposedon diametrically opposite sides of said gantry assembly for supportingsaid gantry assembly respectively on said two support surfaces; andmeans, coupled between said pair of said supports and said two supportsurfaces for moving sad gantry assembly relative to said gantry assemblysupport means and said object support along said longitudinal axis so asto precisely control the position of the gantry assembly relative to theobject support.
 2. An X-ray tomographic apparatus according to claim 1,wherein said means for moving said gantry assembly relative to saidgantry assembly support means and said object support along saidlongitudinal axis includes means for measuring the relative displacementof said gantry assembly relative to said gantry assembly support meansand said object support.
 3. An X-ray tomographic apparatus according toclaim 1, wherein said object support is an patient table having anelongated dimension, said apparatus further including base support meansincluding means for defining said two support surfaces, a firstplurality of wheels for supporting said base support means so that saidgantry assembly and said gantry assembly support means are easilymovable, and a second plurality of wheels for supporting said patienttable so that said patient table is easily movable, and means for fixingsaid patient table relative to said base support means so that saidlongitudinal axis is substantially parallel to the elongated dimensionof said table.
 4. An X-ray tomographic apparatus according to claim 3,wherein said pair of supports includes a pair of arms disposed ondiametrically opposite sides of said gantry assembly and respectivelysupported by said two support surfaces.
 5. An X-ray tomographicapparatus according to claim 4, when said arms pivotably support saidgantry assembly on said two support surfaces.
 6. An X-ray tomographicapparatus according to claim 4, wherein said means for selectivelymoving said gantry assembly relative to said gantry assembly supportmeans and said patient table includes longitudinal translation means forcoupling each of said arms to a respective support surface.
 7. An X-raytomographic apparatus according to claim 6, wherein said longitudinaltranslation means includes a ball screw and nut assembly including aball screw and ball nut for coupling each of said arms to a respectivesupport surface.
 8. An X-ray tomographic apparatus according to claim 7,wherein each of said ball screws is disposed on a respective one of saidsupport surfaces so as to be substantially parallel with saidlongitudinal axis.
 9. An X-ray tomographic apparatus according to claim7, further including means for accommodating a predetermined amount ofnon-parallelism between said ball screws.
 10. An X-ray tomographicapparatus according to claim 7, further including means for separatelydriving each of said ball screws in synchronism so that when said gantryassembly is displaced relative to each of said support surfaces thedisplacement is the same for each of said support surfaces.
 11. An X-raytomographic apparatus according to claim 10, wherein said means forseparately driving each of said ball screws includes a stepper motor,and means for simultaneously operating said stepper motors so that theyare driven at the same speed.
 12. An X-ray tomographic apparatusaccording to claim 11, wherein said stepper motors are reversible sothat each of said ball screws can be driven in either rotationaldirection.
 13. An X-ray tomographic apparatus according to claim 1,further including means for pivoting said gantry assembly relative tosaid gantry assembly support means about an axis substantially normal tosaid longitudinal axis so that said scanning plane can be pivotablymoved to an adjustable angle to the longitudinal axis.
 14. An X-raytomographic apparatus according to claim 13, wherein said pair ofsupports includes a pair of arms disposed on diametrically opposite idesof said gantry assembly and respectively supported by said two supportsurfaces, further wherein said means for pivoting said gantry assemblycomprises means for pivoting said gantry assembly about said arms. 15.An X-ray tomographic apparatus according to claim 14, further includingmeans for controlling and measuring the angle of said gantry assemblyrelative to said longitudinal axis.
 16. An X-ray tomographic apparatusaccording to claim 15, wherein said means for pivoting said gantryassembly about said arms includes a screw element coupled to said gantryassembly support means and a pivotable arm member coupled to said gantryassembly, wherein one end of said arm engages said screw element so asto move along said screw element as said screw element rotates, and theother end of said arm is coupled to said non-rotatable support.
 17. AnX-ray tomographic apparatus according to claim 1, wherein said objectsupport is a patient table.
 18. An X-ray tomographic apparatus accordingto claim 1, wherein said object support is a patient chair.
 19. An X-raytomographic apparatus according to claim 1, wherein said object supportincludes a support for supporting a limb.
 20. X-ray tomography apparatuscomprising in combination:(a) an object support having an elongateddimension; (b) X-ray source and X-rays detection means for use informing a tomographic image; (c) an annular gantry assembly comprising agantry frame, and a rotatable disk for rotatably supporting at least theX-ray source so that said X-ray source rotates about an axis of rotationrelative to the gantry frame during operation; (d) means for rotatingsaid disk about said axis of rotation so as to define a scanning plane;(e) cart means for portably supporting said gantry assembly, said cartmeans including two upwardly extending members flanking the outercircumferential wall of said gantry assembly; (f) lateral displacementmeans for coupling said gantry assembly to said upwardly extendingmembers so that said gantry assembly can selectively move in each of twoopposite directions, relative to said two upwardly extending memberssubstantially parallel to the elongated dimension of said objectsupport; and (g) activation means for activating said lateraldisplacement means.
 21. Apparatus according to claim 20, furthercomprising control means for monitoring and adjusting the position ofsaid gantry assembly relative to said cart.
 22. Apparatus according toclaim 21, wherein said control means comprises potentiometer meanscoupled to said activation means.
 23. Apparatus according to claim 20,wherein said activation means comprises at least one reversible motorand said lateral displacement means comprises at least a first screwmeans coupled to said motor and at least fit first displacement memberfixedly couple to said gantry assembly, farther wherein said first screwmeans engages said first displacement member such that rotation of saidscrews means by said motor results in movement of said firstdisplacement member parallel to said elongated dimension of said objectsupport.
 24. Apparatus according to claim 23, wherein said cart meansincludes rolling means so that said gantry assembly can be transportedby rolling said cart.
 25. Apparatus according to claim 24, wherein saidrolling means comprises a plurality of wheels.
 26. Apparatus accordingto clam 20, further including means for tilting said gantry assembly soas to tilt said scanning plane relative to the elongated direction ofsaid object support.
 27. Apparatus according to claim 26, wherein saidtilting means comprises angular displacement means for two-way movementof a second displacement member relative to said gantry assembly along atrack generally parallel to said axis of rotation, linkage means forcoupling said second displacement member to said gantry assembly, andsecond activation means for activating said angular displacement means.28. Apparatus according to claim 27, wherein said second activationmeans comprises a reversible motor and said angular displacement meanscomprises second screw means coupled to said motor, further wherein saidsecond screw means engages said second displacement member such thatrotation of said screw means by said motor results in movement of saidsecond displacement member along said second track.
 29. X-ray tomographyapparatus comprising in combination:(A) an object support having anelongated dimension; (B) a gantry assembly including:(a) X-ray sourceand X-ray detection means for use in forming a tomographic image; (b) anannular gantry assembly comprising a gantry frame, and a rotatable diskfor rotatably supporting at least the X-ray source so that said X-raysource rotates about an axis of rotation relative to the gantry frameduring operation; and (c) means for rotating said disk about said as ofrotation so as to define a scanning plane; (C) cart means for supportingsaid gantry assembly, said cart means comprising:(a) support wheels fortransporting said gantry assembly; and (b) two upwardly extendingmembers flanking diametrically opposite sides of the outercircumferential wall of said gantry assembly, said extending memberssupporting said gantry assembly for lateral movement in a directionparallel to the object support and for pivotal movement about a pivotaxis normal to the direction of said lateral movement; (D) lateraldisplacement means for coupling said gantry assembly to said upwardlyextending members so that said gantry assembly can selectively move ineach of two opposite directions, relative to said two upwardly extendingmembers in a direction substantially parallel to the object support; and(E) means for selectively securing said object to said cart means sothat a tomographic scan can be made of a portion of an object supportedby said object support.
 30. An X-ray tomography apparatus according toclaim 29 further comprising a patient limb support for supporting only aportion of a patient.
 31. An X-ray tomography apparatus according toclaim 30, further including a chair for supporting a patient whose limbis supported by said patient limb support.
 32. An X-ray tomographyapparatus according to claim 30, further wherein said lateraldisplacement means is selectively movable in each of two oppositedirections, relative to said patient limb support. .Iadd.
 33. A methodof generating volumetric image data of an object, said method comprisingthe steps of:providing a tomographic scanning system including (i) anX-ray source and (ii) an X-ray detector for detecting X-rays emitted bythe X-ray source and for generating scan data as a function of thedetected X-rays, at least one of the X-ray source and detector beingrotatable about a rotation axis to generate the scan data; successivelyincrementally positioning the X-ray source and X-ray detector stepwiseat a plurality of successive discrete positions along the rotation axis;at each of the plurality of discrete positions along the rotation axis,generating a set of scan data for the object; and generating thevolumetric image data for the object using the sets of scan datagenerated at the plurality of successive discrete positions..Iaddend..Iadd.34. A method according to claim 33, further including thestep of generating a volumetric image of the object using the volumetricimage data. .Iaddend..Iadd.35. A method according to claim 33, furtherincluding the step of translating the X-ray source and X-ray detectoralong the rotation axis to each of the successive discrete positionsprior to rotating at least one of the X-ray source and detector at eachsuch discrete position to generate the scan data for the discreteposition. .Iaddend..Iadd.36. A method of claim 33, wherein the object isa medical patient undergoing tomographic examination. .Iaddend..Iadd.37.A method of claim 33, wherein at least the X-ray source is mounted on arotatable gantry of the X-ray tomography system, said rotatable gantrybeing translatable along the rotation axis. .Iaddend..Iadd.38. An X-raytomography apparatus for generating volumetric image data of an object,said apparatus comprising:a tomographic scanning system including (i) anX-ray source and (ii) an X-ray detector for detecting X-rays emitted bythe X-ray source and for generating scan data as a function of thedetected X-rays, at least one of the X-ray source and detector beingrotatable about a rotation axis to generate the scan data; means forsuccessively incrementally positioning the X-ray source and X-raydetector system step-wise at a plurality of successive discretepositions along the rotation axis; means for generating a set of scandata for the object at each of the plurality of discrete positions alongthe rotation axis; and means for generating the volumetric image datafor the object using the sets of scan data generated at the plurality ofsuccessive discrete positions. .Iaddend..Iadd.39. Apparatus according toclaim 38, further including means for generating a volumetric image ofthe object using the volumetric scan data. .Iaddend..Iadd.40. Apparatusaccording to claim 38, further including means for translating the X-raysource and X-ray detector along the rotation axis to each of thesuccessive discrete positions prior to rotating at least one of theX-ray source and detector at each such discrete position to generate thescan data for the discrete position. .Iaddend..Iadd.41. Apparatusaccording to claim 40, further comprising a rotatable gantry on which atleast the X-ray source is mounted; and wherein the means for translatingthe X-ray source and the X-ray detector along the rotation axiscomprises means for translating the rotatable gantry along the rotationaxis. .Iaddend..Iadd.42. Apparatus according to claim 38, wherein theobject is a medical patient undergoing tomographic examination..Iaddend..Iadd.43. An X-ray tomographic scan apparatus of the typecomprising: (a) an X-ray source and X-ray detection means for use informing a tomographic image; (b) a gantry assembly including (i) anon-rotatable support, and (ii) means for supporting at least said X-raysource for rotation within a scanning plane about a rotation axisrelative to said non-rotatable support so as to perform a tomographicscan; (c) coupling means for coupling the gantry assembly to an objectsupport for supporting an object positioned in the scanning plane duringa tomographic scan; said apparatus further comprising:gantry assemblysupport means, capable of being fixed relative to said object support,for supporting said gantry assembly so that said gantry assembly ismovable along a longitudinal axis positionable substantially parallel tothe object support, said gantry support means comprising at least twosupport surfaces positioned respectively on opposite sides of saidgantry assembly; a pair of supports disposed on diametrically oppositesides of said gantry assembly for supporting said gantry assemblyrespectively on said two support surfaces; and means, coupled betweensaid pair of said supports and said two support surfaces, for movingsaid gantry assembly relative to said gantry assembly support meansalong said longitudinal axis so as to precisely control the position ofthe gantry assembly relative to the object support when the gantryassembly is coupled to the object support. .Iaddend..Iadd.44. An X-raytomographic apparatus according to claim 43, wherein said means formoving said gantry assembly relative to said gantry assembly supportmeans along said longitudinal axis includes means for measuring therelative displacement of said gantry assembly relative to said gantryassembly support means. .Iaddend..Iadd.45. An X-ray tomographicapparatus according to claim 43, wherein said object support is apatient table having an elongated dimension positionable along saidlongitudinal axis. .Iaddend..Iadd.46. An X-ray tomographic apparatusaccording to claim 45, further comprising base support means includingmeans for defining said two support surfaces, a first plurality ofwheels for supporting said base support means so that said gantryassembly and said gantry assembly support means are easily movable, anda second plurality of wheels for supporting said patient table so thatsaid patient table is easily movable, and means for fixing said patienttable relative to said base support means so that said longitudinal axisis substantially parallel to the elongated dimension of said table..Iaddend..Iadd.47. An X-ray tomographic apparatus according to claim 43,wherein said pair of supports includes a pair of arms disposed ondiametrically opposite sides of said gantry assembly and respectivelysupported by said two support surfaces. .Iaddend..Iadd.48. An X-raytomographic apparatus according to claim 47, wherein said arms pivotablysupport said gantry assembly on said two support surfaces..Iaddend..Iadd.49. An X-ray tomographic apparatus according to claim 47,wherein said means for selectively moving said gantry assembly relativeto said gantry assembly support means includes longitudinal translationmeans for coupling each of said arms to a respective support surface..Iaddend..Iadd.50. An X-ray tomographic apparatus according to claim 49,wherein said longitudinal translation means includes a ball screw andnut assembly including a ball screw and ball nut for coupling each ofsaid arms to a respective support surface. .Iaddend..Iadd.51. An X-raytomographic apparatus according to claim 50, wherein each of said ballscrews is disposed on a respective one of said support surfaces so as tobe substantially parallel with said longitudinal axis..Iaddend..Iadd.52. An X-ray tomographic apparatus according to claim 50,further including means for accomodating a predetermined amount ofnon-parallelism between said ball screws. .Iaddend..Iadd.53. An X-raytomographic apparatus according to claim 43, further including means forpivoting said gantry assembly relative to said gantry assembly supportmeans about an axis substantially normal to said longitudinal axis sothat said scanning plane can be pivotably moved to an adjustable angleto the longitudinal axis. .Iaddend..Iadd.54. An X-ray tomographicapparatus according to claim 53, wherein said pair of supports includesa pair of arms disposed on diametrically opposite sides of said gantryassembly and respectively supported by said two support surfaces,further wherein said means for pivoting said gantry assembly comprisesmeans for pivoting said gantry assembly about said arms..Iaddend..Iadd.55. An X-ray tomographic apparatus according to claim 54,further including means for controlling and measuring the angle of saidgantry assembly relative to said longitudinal axis. .Iaddend..Iadd.56.An X-ray tomographic apparatus according to claim 55, wherein said meansfor pivoting said gantry assembly about said arms includes a screwelement coupled to said gantry assembly support means and a pivotablearm member coupled to said gantry assembly, wherein one end of said armengages said screw element so as to move alone said screw element assaid screw element rotates, and the other end of said arm is coupled tosaid non-rotatable support. .Iaddend..Iadd.57. An X-ray tomographicapparatus according to claim 43, wherein said object support is apatient chair. .Iaddend..Iadd.58. An X-ray tomographic apparatusaccording to claim 43, wherein said object support includes a supportfor supporting a limb. .Iaddend.